This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-59984, filed Mar. 8, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a window glass antenna apparatus for vehicles which is mounted on a window glass of a vehicle such as an automobile.
There is a window glass antenna apparatus for automobiles as the most typical conventional antenna apparatuses for vehicles. This type of antenna apparatus includes a thin, narrow strip conductor provided on a window glass (usually a window glass of a rear window) of an automobile, and the conductor is employed as an antenna.
Recently a defogger has been provided almost all over the rear window glass of an automobile to serve as a heater for defogging the window glass. The antenna therefore has to be mounted in a limited space between the defogger and the window frame.
The above-described conventional window glass antenna apparatus for automobiles has a problem that its receiving sensitivity cannot be obtained sufficiently in the AM or FM band since a space for mounting the antenna is limited. The apparatus has another problem that a tuning operation for optimizing reception performance by adjusting the shape and arrangement of the antenna is difficult to perform and thus requires a long period of time.
In order to resolve the above problems, applicant has developed the following window glass antenna apparatus for vehicles and filed it as Japanese Patent Application No. 10-282870. The antenna apparatus comprises a defogger mounted on a window glass of a vehicle to defog the glass, a member for causing the defogger to serve as a slot antenna, and a driven antenna arranged close and opposite to the defogger with a given gap therebetween in such a manner that one side of the driven antenna is mutually coupled to that of the defogger.
The window glass antenna apparatus of Japanese Patent Application No. 10-282870 has the advantages that its receiving sensitivity is high across a wide frequency band and its tuning operation is easy to perform. However, it still has the following problem to be solved.
In order to cause the defogger to function as an antenna adaptable to a plurality of wide frequency bands, it is desirable to make a short circuit between the defogger and the window metal frame at a high frequency. It is thus unclear where the defogger and window metal frame should be short-circuited. Consequently, it is likely that a desired antenna characteristic will not be obtained according to the location of a short circuit.
The object of the present invention is to provide a window glass antenna apparatus for vehicles which has the advantages that its receiving sensitivity is high across a wide frequency band and its tuning operation is easy to perform and which can be mounted exactly on a window glass of an automobile to constantly obtain a desired antenna characteristic.
To attain the above object, there is provided a window glass antenna apparatus for vehicles, comprising a defogger having a pair of bus bars and constituted of a thin, narrow strip conductor, for defogging a window glass of a vehicle, the bus bars being arranged at both side ends of the window glass and opposite to each other with a gap between a window metal frame of the vehicle and the bus bars, a driven antenna having a predetermined height and arranged close and opposite to the defogger with a clearance therebetween, one side of the driven antenna being mutually coupled to one side of the defogger, and a short circuit section for causing a short circuit between each of upper ends of the bus bars and the window metal frame at a high frequency. The short circuit section is constituted of a pair of short circuits configured to cause a short circuit between each of lower ends of the bus bars of the defogger and the window metal frame at a high frequency.
The short circuit section is constituted of a single short circuit for causing a short circuit between a lower central part of the defogger and the window metal frame at a high frequency.
The short circuit section is constituted of a pair of short circuits configured to cause a short circuit between each of middle right and left ends of the defogger and the window metal frame.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.